JP2020521165A - Ultra-thin flexible thin film filter with spatially or temporally varying optical properties and method of making the same - Google Patents

Abstract

A method of making an optical filter film with various optical properties is a step of stretching a multi-layer polymer preform into an optical filter and a member of the group consisting of heat, pressure, tension, and stretching speed. Changing at least one environmental condition, the at least one environmental condition being changed over time and/or over a distance, or both, to produce a change in layer thickness within the optical filter. Including. The preform is drawn through a furnace, which applies heating power to the preform that varies across the width of the furnace or over time or across the width and time. The preform is also drawn through the oven while the draw rate varies across the width of the oven or over time or over the width and over time.

Description

The present application relates to a method of making a thin film filter having optical properties that change at least over a length or width or over time and a method of making such a flexible thin film filter.

Multispectral and hyperspectral imaging have applications in several fields, such as drug development and safety testing, biomicroscopy, forensic analysis, security, environmental monitoring, textile production, food safety and quality control, and waste. It is a relatively new imaging method that is growing for recycling and sorting.

Hyperspectral imaging (HSI) is a technique for investigating the situation and extracting detailed information by combining imaging (imaging) and spectroscopy (spectroscopy). HSI, also called Imaging Spectroscopy, is a powerful data processing-intensive method that creates a "data cube" that contains information about the properties of hundreds to thousands of narrow wavelength targets within the field of view of the system. is there.

Hyperspectral imaging differs from related art multispectral imaging primarily in the number of wavelength bands and how the wavelength bands are narrow. Multispectral techniques typically produce 2-D images in a few to hundred wavelength bands, each covering tens of nanometers. Multispectral imaging combines 2-5 spectral imaging bands of relatively wide bandwidth into a single optical system.

In contrast, hyperspectral imaging yields large 3-D cubes of hundreds or even thousands of images, each with dimensions (x, y, λ) in the range of only a few nanometers. .. Multispectral imaging is quick and easy to process on this small data set, while hyperspectral imaging provides very high complexity of data, high resolution spectrum, and is versatile and satellite-friendly. There are many applications beyond the use of imaging.

Most techniques for both hyperspectral and multispectral imaging require filters that vary either spatially or temporally.

Some configurations use filters fixed on multiple detector arrays to simultaneously capture multiple image frames in different spectral bands. Some other forms use a filter wheel or a linear stage in front of a single detector array to sequentially capture the image frames, with various filters sequentially covering the detector array. Some forms use liquid crystal based filters, which are tuned using electrical stimulation of the liquid crystal cavity index of refraction to shift their passband wavelengths.

The trending method utilizes a linear filter that changes separately or continuously and the spectrum gradually shifts from one end of the filter to another. These filters are typically edge filters (short pass or long pass) or band pass filters, where the edge or center wavelength sweeps across a wide spectral range on a single filter.

Prior art

Tunable filters are made by a high degree of variation in the vacuum deposition process, which is frankly expensive, which makes them significantly more expensive than comparable uniform filters. While high performance uniform filter fabrication is very expensive and limited in scalability, variable filter fabrication is more costly due to the complex motion or lithographic steps added to the deposition process. Expensive. In addition, traditional tunable filters are manufactured on thick glass substrates, which makes these tunable filters suboptimal for optical systems that require light weight or compactness.

U.S. Patent No. 9,597,829 and U.S. Patent Application Publication No. 2017/01444915 describe a method of making a thin film optical filter using thermal drawing of a structured preform. It has been described. This method allows the fabrication of thin film interference optical filters in the form of flexible ultra-thin films and sheets, all made of plastic. This method provides two significantly higher levels of traditional vacuum-plated thin-film filters by providing a significantly higher scalability and an ultra-thin filter that can be curved and contoured in addition to being fairly compact. Solve the drawbacks.

US Pat. No. 9,597,829 U.S. Patent Application Publication No. 2017/0144915

According to a first aspect of the present invention, a method of making an optical filter film having various optical properties comprises the steps of stretching a multi-layer polymer preform into an optical filter state, heat, pressure and tension. , And at least one environmental condition that is a member of the group consisting of stretching speed, the at least one environmental condition being changed over time and/or over a distance, or both, and within the optical filter. Further comprising the step of causing a change in layer thickness. Specific examples include one or more of the following features.

The at least one environmental condition can be heat, the preform is drawn through a furnace, and the furnace changes into the preform over the width of the furnace or over time or over the width and over time. Add heating power. To this end, the method may further include the step of positioning the heaters on opposite sides of the preform, wherein the opposite sides of the preform extend along the direction of stretching of the preform and the width of the furnace. Extends across the stretch direction, and the method further comprises stretching the preform in the stretch direction in an oven.

At least one of the heaters may apply heating power to the preform that varies along the width of the furnace. For example, heating power may be varied by positioning at least one heater such that the heater makes an acute angle with the preform.

Additionally or alternatively, the heating power may be varied by heating at least one heater to different temperatures along the width of the furnace. Additionally or alternatively, the heating power of the furnace may be varied at least locally over time while the preform is being drawn through the furnace.

Additionally or alternatively, the at least one environmental condition may be a draw rate, and the preform is drawn through a furnace such that the draw rate is across the width of the furnace or over time or width. A thin film in a zone that is stretched through a furnace while undergoing overall and changing over time, thereby being exposed to a higher stretch rate than in a zone that is exposed to a low stretch rate and has a thick membrane layer. Produces a multilayer film with layers.

For example, the draw rate may be higher on one side of the furnace width than on the opposite side, or the draw rate may be higher on the middle portion of the furnace width than on the lateral sides.

Additionally or alternatively, the draw rate may alternate between a low draw rate and a high draw rate over time.

The method comprises cutting at least one piece from the multilayer film at a boundary region forming a transition region from one of the zones with a thin film layer to one of the zones with a thick film layer. It is better to include more.

Gradient layer thickness is also achieved by heat and tension, in which case the preform is stretched through a furnace that applies heating power to the preform to form an intermediate filter membrane, which in turn , Subjected to heat and tension at least in the longitudinal or transverse direction of the intermediate filter membrane at the designated location, so that the intermediate filter membrane is stretched and the layer thickness is permanently reduced at the designated location, thereby Forming an optical filter with locally reduced layer thickness.

Further details and advantages will become apparent from the following description of various embodiments with reference to the accompanying drawings. The drawings are provided herein for purely illustrative purposes and are not intended to limit the scope of the invention.

1 is a first schematic diagram of an apparatus for thermally stretching a multilayer thin film filter. It is a figure which shows the 1st Example which distributes a heating element over the width of a furnace. It is a figure which shows the 2nd Example which distributes a heating element over the width of a furnace. FIG. 6 illustrates another device that provides heat that varies over the width of the furnace. FIG. 6 illustrates another device that provides heat that varies over the width of the furnace. FIG. 6 illustrates another device that provides heat that varies over the width of the furnace. FIG. 6 illustrates another device that provides a grading thickness across the width of the furnace. FIG. 6 illustrates another device that provides a varying thickness across the width of the furnace. FIG. 6 illustrates another device that provides a grading thickness across the width of the furnace. It is a schematic sectional drawing of a multilayer thin film filter. It is a figure which shows one of the partially expanded sectional views of a multilayer thin film filter. It is a figure which shows another example of the partial expanded sectional view of a multilayer thin film filter. It is a figure which shows another example of the partial expanded sectional view of a multilayer thin film filter. 3 is a schematic of one of two embodiments of a device for varying the thickness of a thin film filter. 6 is another schematic diagram of two embodiments of an apparatus for varying the thickness of a thin film filter. FIG. 6 illustrates an example of varying at least the thickness or width of the filter membrane by varying the velocity of the filter membrane moved through the furnace. FIG. 6 illustrates an example of varying at least the thickness or width of the filter membrane by varying the velocity of the filter membrane moved through the furnace. 3 is a schematic diagram of an apparatus for varying at least the thickness or width of a membrane filter by applying heat and tension. 3 is a schematic diagram of an apparatus for varying at least the thickness or width of a membrane filter by applying heat and tension. 3 is a schematic diagram of an apparatus for varying at least the thickness or width of a membrane filter by applying heat and tension.

The present application describes various variations of thermally stretching a thin film optical filter to make a tunable filter. The present application also discloses various post-processing methods to modify a uniform filter made by such a hot drawing method to make various filters.

Method of making a tunable filter during a hot drawing process

Referring now to FIG. 1, a preform 10 has been moved longitudinally through a furnace 12 to thermally stretch a thin film multilayer filter membrane, which in FIG. 1 is perpendicular to the image plane. It corresponds to various directions. The term "preform" is used to describe a polymer block that includes the optical layers of the final filter film, but has a layer thickness that is many times greater than the final thickness of the resulting layer of the filter film. ing.

The furnace 12 extends across the width of the furnace 12 on opposite sides of the preform 10 to heat the preform 10 as it moves through the furnace 12 in and out of the image plane of FIG. It has a heater 14 arranged. To produce a film or sheet having a uniform spectral shape, the furnace 12 provides a correspondingly uniform heat density across the furnace 12. However, altering the heat density along the heater 14 extending across the width of the furnace 12 can help make a tunable filter. High temperatures increase the flow of polymeric material and increase the thickness of the stretched film, as compared to low temperatures, for the same stretch rate. In this case, this change in thickness causes a change in the spectral properties in the filter, mainly in the form of shifted spectra with the same spectral shape.

In the two examples shown in FIGS. 2A and 2B taken along the line AA′ shown in FIG. 1, the heater 14 has a heating element 16 shown as a coil. In particular, the illustration of the heating element 16 as a coil is not intended to exclude other types of heating elements 16, such as resistive heating elements having different shapes. In the illustrated embodiment, the heater 14 has a graded heat density across the width of the furnace 12, this width direction being referred to as the horizontal direction. In this regard, the width of the furnace 12 is arranged horizontally such that gravity affects the preform 10 such that the resulting membrane and softened polymeric material are uniformly distributed across the width of the furnace 12. It doesn't run away.

In FIGS. 2A and 2B, the large amount of heat added by each heater 14 is represented by two heating elements 16 shown at a common location across the width, and a small amount of heat at a given location. It is represented by only one heating element 16. This representation is purely symbolic, a large amount of heat generation and a small amount of heat generation can each be achieved by a single heating element 16 or many heating elements 16. The arrangement only exhibits high heat output where higher temperatures are desired than where lower heating temperatures are desired.

FIG. 2A shows the alternating heat density represented by a sinusoidal temperature curve with alternating peaks and valleys of temperature T over the width W of the furnace reproduced below the schematic of the apparatus, and FIG. Shows a configuration in which one side of the heater 14 is in a higher temperature state than the other side of the heater 14, which is indicated by a temperature curve having peaks on the left side and valleys on the right side. In particular, even the troughs of the temperature curve represent temperatures above ambient room temperature because these low power heating zones still include heating elements 16 that raise temperature T above ambient temperature. Because there is. The amplitude of the heat density at various locations on the preform 10 (where the heating power reaches the preform at a particular location) and the rate of change in density per unit length of the heater 14 across the width of the furnace 12 is the layer thickness. And determine the specific spectral profile and dimensions of the resulting filter membrane or sheet by determining the change in layer thickness of the resulting filter membrane. The segment of the filter membrane or sheet in the transition region between different zones of heating power may be cut out of the resulting membrane into a small shape to be used as a tunable filter. The spatial profile of the filter change follows the temperature curve of the heating zone, where the hot heating zone provides greater filter film thickness than the cold heating zone.

In another example, the heating zones may be realized by heating elements 16 that are individually controllable to set a predetermined local heating power density, thereby creating different heating profiles across the furnace 12. If all heating zones are set to the same temperature to reach the preform (heating power density), a uniform filter membrane or sheet will result.

In another embodiment shown in FIGS. 3A, 3B, and 3C, the hot draw furnace 12 has the option of changing the angle it makes with at least one preform 10 of the heaters 14. 3A, 3B, and 3C show different configurations of angled or tilted heater 14 in furnace 12. Varying the distance of the preform 10 from one of the heaters 14 that provides a uniform heater temperature across each width of the heater 14 changes the heating power density at the location of the preform. Changes, thus resulting in varying effective temperatures applied to the preform 10. Thus, by tilting the position of the heater 14 with respect to the preform 10, the material viscosity in the preform 10 changes across the width of the furnace 12. Therefore, when the preform 10 is stretched through the furnace 12, the resulting filter membrane or sheet has different optical properties across the width of the furnace 12 due to the different layer thicknesses. become.

In FIG. 3A, if only one of the two heaters 14 is positioned at an acute angle α with the surface 18 of the preform 10, then in most cases the layers of material will vary in thickness and the layers of material will vary. Are located near one surface 18 of the preform 10 facing the inclined heater 14. In FIG. 3B, a thermal gradient is utilized from each of the two heaters 14 by positioning each of the two heaters 14 at an angle α,β with the surface 18,20 of the preform 10, respectively. The angles α and β may be selected independently of each other, or they may be the same and mirror image relationship to each other as shown in FIG. 3B. In FIG. 3C, the membrane layer near one surface 20 has a reduced thickness from left to right, and the membrane layer located near the opposite surface 18 has an increased thickness from left to right. The reason is that one of the heaters 14 makes an angle α to increase its distance from the preform from left to right and the other heater 14 makes an angle α from the preform from left to right. Because it reduces that distance. The angles α, β formed by the heater 14 and the preform are peculiar to each furnace 12, and these angles can be empirically determined by calibration. For example, the angles α, β depend on the amount of heat dissipated from the heater, which is affected by the geometry and material of the furnace 12 and affects the effective temperature applied to the preform 10. Exert.

Another example of varying the effective temperature or heat heating power density across the furnace 12 is a non-contact element placed in front of the uniform heating element 16 to control the profile of heat radiation transferred from the heater 14 to the preform. Includes uniform insulation or heat conductor material. To create this non-uniformity, one or more properties of the material disposed between the heater 14 and the preform may be varied, such as thickness, porosity, or face dimension. ..

Changes to the preform 10 may be made to make the tunable filter without making any changes to the furnace 12. One possible form is shown in FIGS. 4A-4D and another is shown in FIGS. 5A and 5B. When the preform 10 having an asymmetric starting geometry is stretched while keeping the rate at which the preform 10 is stretched through the furnace 12 and the tension applied to the entire preform unchanged, the resulting filter membranes have different thicknesses. , And therefore of a gradually changing spectral shape. An example of a preform having a wedge geometry can be seen in Figures 4A, 4B, and 4C. In this case, the wedge-shaped geometry of the preform 10 results in a thicker film on one lateral side, and the gradually changing thickness is thinner on the other lateral side. This is because there is much material of the original preform 10 on the side of the thicker wedge. In this case, the gradual change in thickness results in various optical properties throughout the filter. The wedge configuration may be such that it makes two acute angles α, β between each adjacent heater 14 and its surface 18, 20 as shown in FIG. 4A, or parallel to one of the heaters It may be arranged in the furnace such that there is only one acute angle α between the surface 18 and the heater 14 next to it. Further, as shown in FIG. 4C, the wedge-shaped preform 10 may have a trapezoidal cross-section, in which case the apex of the wedge is truncated.

In particular, the wedge-shaped preforms of Figures 4A, 4B, or 4C may be combined with heaters 14 that are angled with respect to one another, such as shown in Figures 3A or 3B, so that the heaters Both 14 can be parallel to their respective surfaces 18, 20 or the heaters are spaced more widely from one another on the thin side of the preform than on the thicker side of the preform. This is because the heating power density required by the thinner side is low.

Other modifications to the geometry can be utilized for the layers found in the preform. FIG. 5A is a cross-sectional view of the multi-layer preform 10, and FIGS. 5B, 5C, and 5D are enlarged views showing the rectangular details marked in FIG. 5A and three examples of non-uniform layer configurations. In this case, the two different hatchings represent, in this case, two different alternating layers of material 22, 24 that make up two layers of the resulting multilayer structure of the thin film filter. .. The remainder of the multi-layer structure may be formed of the same alternating or stacked layers of different materials. The uniform application of heat to the preform 10 including the layers 22, 24 in contact with each other at the curved interface surface results in layers having a thickness that is the same as the thick layers 22, 24 of the preform 10. A filter membrane provided is obtained. However, the layer thickness is made significantly smaller than the layer thickness of the preform 10.

Another draw parameter that can be varied across the film to affect the film thickness across the film to produce a tunable filter is the draw tension and/or draw speed across the furnace. FIGS. 6A and 6B show two possible tension profiles across the furnace 12, where a higher draw rate increases the tension of the heated and softened preform 10 and thus the thin film 26. Created and vice versa. FIG. 6A shows a linear profile that can be achieved by pulling one side of the membrane faster than the other, resulting in a gradual increase in thickness from left to right, and thus the membrane. A graded spectral shape is obtained over the whole. In a similar manner, FIG. 6B shows that the film is pulled quickly from the middle section and late at the edge, resulting in a thin film in the middle and a gradual increase in thickness as the thickness approaches the edge. The tension profile is shown.

To achieve a transversely varying draw rate, uneven pressure may be applied across the preform width between the opposing rollers that pull the membrane 26. Non-uniform pressure is due to the fact that the rollers are pressed against each other with greater force on one side than the other, so that one lateral side has a higher pressure than the opposite lateral side. Is good. In order to achieve different stretching speeds in the central part of the preform 10 than in the lateral parts, in particular rollers which are not perfectly straight are used. The core of the roller may be slightly bent or the rubber on the roller may be trimmed to create an arbitrary thickness profile, resulting in a consistent pressure (and velocity) profile across the width. .. To achieve different pressure distributions across the width of the rollers and across the furnace to achieve different and variable distributions of draw speed, individually adjustable pressures forming rollers or roller segments across the width. And/or it may be formed at a stretching speed. In general, the rollers or individual roller segments may be made of an elastically compressible material to improve pressure distribution. The rollers or roller segments can have roller diameters that are graded or different from one another, so that at large diameters, large pressures are exerted on the preform, which, due to the long roller circumference, are also locally localized. A relatively high stretching speed is achieved.

In another example, increasing stretching speed and tension over time can be used to provide a spectral shift along the stretched filter membrane 26 or sheet. FIG. 7A shows a stretching process in which the stretching speed is varied between a first speed V1 and a second speed V2 over time. FIG. 7B demonstrates the effect of this wobbling stretching rate on the film. By varying the draw rate over time, as opposed to varying the tension throughout the furnace, the effect is on the thickness of the membrane 26 in the longitudinal direction rather than the transverse direction.

FIG. 7B is a sectional view showing the thickness of the resulting filter film 26. Increasing the stretching rate and then gradually decreasing this rate while applying the same tension across the horizontal at each time interval results in an increase or decrease in the longitudinal thickness of the membrane 26. Changes in film thickness also change the spectral properties of the film, as changes in film thickness proportionally affect the thickness of the layers that make up the film.

This variation in film thickness provides an additional optional alternative for making tunable filters. The transition region between different drawing speeds forms different filters along the vertical direction. The gradient or step size that changes the draw rate relative to the feed rate or resistance applied to the preform defines a length along the resulting membrane 26 on which the spectral shift occurs. A slow speed change results in a slowly changing filter and vice versa. The width of the resulting filter membrane 26 may also change with a gradual stretching speed, but this effect is of much smaller proportion than the change in thickness.

Post-processing method for making tunable filters

Making a filter with various properties, one example of such post-processing treatment of a uniform filter membrane 26 or sheet is shown in FIGS. 8A, 8B, and 8C. After stretching the preform 10 into an intermediate filter membrane 26 or sheet (which itself may already have formed a flat optical filter), then the zones 26 of the membrane 26 or sheet are removed. Heating to a temperature close to the glass transition temperature of the material may be sufficient to soften the film 26 to cause permanent set. While the membrane material is still hot, a pulling force F may be applied to the opposite lateral or longitudinal ends of the membrane 26, resulting in stretching of the membrane as seen in FIG. 8A. Stretching the membrane in one direction results in a reduction in dimension in the other two dimension directions perpendicular to the stretching direction of the pulling force F as shown in FIGS. 8B and 8C. The boundary region 30 of the heated region 28, where the transition occurs between the stretched and unstretched portions of the membrane 26, forms a region where the layer thickness varies and thus the optical properties of the filter membrane 26 vary. The geometry of heating zone 28, the temperature of heating zone 28, and the distance of the heat generator from the filter membrane define the filter spectral shift rate per unit length. For example, a large distance of the heat generator from the surface of the filter membrane will result in a more gradual change in the filter characteristics, thus creating a boundary region 30 wider than a small distance that adds highly localized heat.

In another embodiment, a section of the filter membrane, which may be uniform or manufactured to have a non-uniform thickness, may be placed in a customized mold or press, such as The mold or press heats the filter membrane slightly. The mold or press can apply a gradual pressure to various parts of the filter membrane, resulting in slight changes in the filter thickness and its spectral characteristics. This method can be used with molds having two-dimensional variations to make two dimensionally different filters. For example, using a mold press that replicates the curvature of the lens has two purposes: (1) slightly bending and stretching the filter film to conform the filter to the lens surface without stressing the film. (2) It serves the purpose of slightly shifting the spectral characteristics of the filter with a radial pattern that compensates for the effect of the angle of incidence on the spectral shape of the filter for light striking different parts of the lens at different angles.

In another embodiment, a uniform filter membrane or sheet may be placed on a surface that may be slightly heated. This surface may have a wedge-shaped bevel (or a non-uniform surface with different depth profiles) to allow the filter membrane to rest on this bevel with the surrounding sections being flat and easy. Good to place. A cold or heated roller then rolls over the filter membrane or sheet, gradually rolling the filter membrane or sheet into various angles as the roller travels through the beveled area along the length of the area. Compress. This non-uniform pressure exerted on the filter with the filter near the softening point of the material causes a change in the filter layer thickness and is therefore identical to the non-uniform (graded) section of the substrate surface It can cause a spectral shift that follows the depth profile.

How to change the filter over time

All of the methods and examples disclosed above relate to the fabrication of spatially varying filters with various spectral features across the physical dimensions of the filter, ie, the longitudinal and/or lateral dimensions. ..

Another way to change the characteristics of the filter is by heating. All materials have a finite coefficient of thermal expansion (CTE). This causes a change in the thickness of the thin film layer, which results in a shift of the transmission spectrum curve (thermal spectrum drift). In traditional hard-coated filters, this effect has minimal impact on the spectral properties due to the low CTE of the hard oxides and other materials used in hard-coated thin film filters. However, most thermoplastic polymers used to thermally stretch filter membranes and sheets have a relatively high CTE, which results in significant spectral drift due to temperature fluctuations. This effect may be placed under control which is used as a method of shifting the spectrum of the filter as it changes the filter characteristics over time. The filter properties change as a function of local temperature, so that the optical properties are transient and changeable during use of the filter membrane.

This can be accomplished in various ways. In one form, the filter membrane or sheet may be provided in a miniature temperature controlled holder, which is capable of controllably changing the temperature around the filter. Alternatively, the filter membrane or sheet may be placed against (or laminated to) a temperature controlled glass substrate. This temperature control can be achieved by mounting heating and cooling plates (eg, thermoelectric generators or modules) around the glass outside the filter openings. This can also be achieved by laminating the filter on a glass substrate with a transparent conductive coating (eg indium tin oxide, ITO) with a high resistance that can cause heating due to surface current generation. An example of how to provide a filter membrane in a holder or frame or on a substrate is described in WO 2017/180828, which is incorporated by reference, the entire content of which is hereby incorporated by reference. Part.

These temporary heat induction filter modifications can be applied to both uniform and tunable filters. Filters with temporally changing optical properties are particularly useful in applications that do not require rapid changes in optical properties. For rapid changes, filters with spatially changing properties can be movably mounted, so that moving the filter perpendicular to the viewing direction changes its optical properties.

In summary, we have provided various options for manufacturing multilayer filter membranes with various optical properties. Furthermore, a method of modifying the optical filter after the stretching process has been described. Combining two or more of these options and methods allows more complex modifications if desired. For example, it should be understood that post-processing procedures can be applied to membranes whose properties are modified during the stretching stage of the membrane. Also, temporary modification can be performed following permanent set by applying heat. Therefore, all of the provided processes are not mutually exclusive, but complement each other.

Although the above description relates to preferred embodiments of the present invention, the present invention can be modified, modified and changed without departing from the proper scope and fair meaning of the present invention described in the appended claims. It will be understood that there is.

Claims (19)

A method of making an optical filter film with various optical properties, the method comprising the steps of stretching a multilayer polymer preform into an optical filter, and applying heat, pressure, tension, and a stretching rate. Changing at least one environmental condition that is a member of the group, said at least one environmental condition being changed over time and/or over a distance, or both, and a layer thickness within said optical filter. The method further comprising causing a change in depth. The at least one environmental condition is heat and the preform is stretched through a furnace that causes the preform to extend over the width of the furnace or over time or over the width and over time. The method of claim 1, wherein varying heating power is applied to. The method further comprises positioning heaters on opposite sides of the preform, the opposite sides of the preform extending along a stretch direction of the preform, and the width of the furnace extending across the stretch direction. ,
The method of claim 2, further comprising the step of stretching the preform in the furnace in the stretching direction. The method of claim 3, wherein at least one of the heaters applies heating power to the preform that varies along the width of the furnace. The method of claim 4, wherein the heating power is varied by positioning the at least one heater such that the heater makes an acute angle with the preform. The method of claim 4, wherein the heating power is varied by heating the at least one heater to different temperatures along the width of the furnace. The method of claim 2, further comprising varying the heating power of the furnace at least locally over time while the preform is being drawn through the furnace. The at least one environmental condition is a draw rate and the preform is such that the draw rate at which the preform is drawn through the oven varies across the width of the oven, or changes over time, or Stretched through the oven across its width and with time variation, thereby having a thin membrane layer in a zone exposed to a higher stretch rate than in a zone having a lower stretch rate with a thick membrane layer The method of claim 1, wherein a multilayer film is produced. 9. The method of claim 8, wherein the draw rate is higher on one side of the width of the furnace than on the opposite side. 9. The method of claim 8, wherein the draw rate is higher in the central portion of the width of the furnace than in the lateral sides. 9. The method of claim 8, wherein the draw rate alternates between a low draw rate and a high draw rate over time. Cutting out at least one piece from the multilayer film at a boundary region forming a transition region from one of the zones with the thin film layer to one of the zones with the thick film layer. 9. The method of claim 8, further comprising: The at least one environmental condition is heat and tension, the preform is drawn through a furnace, the furnace applying heating power to the preform to form an intermediate filter membrane, the method comprising: Subjecting the intermediate filter membrane to heat at specific locations and to tension in at least the longitudinal or lateral direction of the intermediate filter membrane, and to form the optical filter with a locally reduced layer thickness, The method of claim 1, further comprising stretching the intermediate filter membrane until the layer thickness is permanently reduced at the particular location. 14. The method of claim 13, wherein the step of stretching the intermediate filter membrane is performed while the intermediate filter membrane is still hot after passing through the furnace. The method of claim 1, wherein the multilayer polymeric preform comprises a preform layer of non-uniform thickness. The method of claim 1, wherein the multilayer polymeric preform has a wedge or trapezoidal cross section. The optical filter made by stretching the multilayer polymer preform is an intermediate optical filter, and the step of changing at least one environmental condition comprises placing the intermediate optical filter in a customized mold or press. The method of claim 1, wherein the method is carried out after the stretching step by heating and by heating the filter membrane. 18. The method of claim 17, further comprising applying a spatially graded pressure by the mold or press to various portions of the intermediate optical filter and causing a thickness change to form a final optical filter. Method. The mold or press has a curved surface, and the method comprises applying pressure to the intermediate optical filter by the mold or press to cause a change in shape to form a final bent or domed optical filter. 18. The method of claim 17, further comprising the step of:

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